Industrial process control systems are used to monitor and control industrial processes used to produce or transfer fluids or the like. In such systems, it is typically important to measure “process variables” such as temperatures, pressures, flow rates, and others. Process control transmitters are used to measure such process variables and transmit information related to the measured process variable back to a central location such as a central control room.
One type of process variable transmitter is a pressure transmitter which measures process fluid pressure and provides an output related to the measured pressure. This output may be a pressure, a flow rate, a level of a process fluid, or other process variable that can be derived from the measured pressure. The pressure transmitter is configured to transmit information related to the measured pressure back to a central control room. The transmission is typically over a two wire process control loop, however, other communication techniques are sometimes used, including wireless techniques.
The pressure must be coupled to a process variable transmitter through some type of process coupling. In certain process pressure measurement applications, the pressure transmitter is located remotely relative to a pressurized process fluid, and pressure is physically conveyed from the process fluid to the pressure transmitter through a fluid link using a device called a remote seal. A remote seal is a secondary system that is filled with a substantially incompressible fluid that transmits pressure from the process fluid to the pressure transmitter. Remote seals are typically used in applications where the process fluid has a high temperature, is corrosive, or has some other extreme application or characteristic that could damage or disrupt the pressure transmitter if the pressure transmitter were located too close to the process fluid.